Hi everyone.
I just orderd my sensor parts and was wondering, why there is the most basic information so hard to find on the mainpage and also in the forum: what does PM2.5 and PM10 mean, anyway?
So, for all newbies:
German readers can find this well explained over here:
https://www.bmuv.de/themen/gesundheit/luftreinhaltung/feinstaub
English readers can find it pretty nice explained on this page:
https://www.irceline.be/en/documentation/faq/what-is-pm10-and-pm2.5
Or you do a quick search at wikipedia for particulate matter …
(Using existing knowledge and doing a search are really very underestimated … 
. Copying the same informations again and again isn’t very effective. To keep this up to date with the latest scientific findings we would need to check for these informations regularly. This would bind one of our rarest resources in this volunteered projects, time …)
To be fair though, if you somehow end up by accident on the sensor.community homepage it is unlikely you are going to figure out what it is about. Plus it would be hard to search for particulate matter as it is not even mentioned, if you exclude the pm acronym on the map.
Do not take it the wrong way, this is not to complain. I understand that resources are limited and there are different priorities. I just find that the “just google it” attitude is often misplaced, especially when it is not even obvious what you should search for. 
That’s why I am helping. You are welcome.
But speaking of: there are two mistakes in the assembly guide, maybe you can help to correct them.
A minor one:
“- Push the other pipe onto the first one.”
What other one? At this point there is “another pipe” mentioned for the first (and last) time. Probably the is a “2x” missing before the weather protection pipe in the shopping list. A picture of the ready made case would be good, as well.
A critical one:
Please take a look at the picture where is says " When you are done, this is how it should look like".
Well, I would say it should definitely NOT look like this. In the schematic above you can see that the GND and Voltage wires, connecting the BME280, shall be crossed. In the picture the puple and the brown wire are crossed on the left hand side, but also on the right hand side = double crossed. Which makes it not crossed at all → short circuit.
So, kids: do not try this at home! 
Looks like @nick is no forum member anymore. However, for other people who might get confused:
“- Push the other pipe onto the first one.”
This is about the pipes for the housing (Weather protection, Marley Silent HT Arc DN 75 87°) which needs two. @nick got confused with two pipes and one tube.
A critical one
Me too I have not been aware that there are different breakout boards for the BME280 with different pinouts. For some you need to cross cables, for some not. Maybe that could be mentioned.
Always double check your own hardware and how to connect it!
As far as I know, I am still a member.
Yes, because only one is mentioned in the shopping list. I think that should be corrected. However, so far everyone has to got this on his/her own.
And yes, you probbaly better check the schematic and the borads you have, rather than trusting the picture.
My idea was to mention these two things in the manual to avoid any more confusion.
@nick I couldn’t open your personal infos clicking on your name last time which made me think you left already. Today I can open it!
Important is to connect D3 - SDA, D4 - SDC, GND - GND and 3V3 - VIN, this is right in both pictures. Both is schematic, one for the wireing, one for the mechanical construction. No mistake!
If you read further on you will find out, that one can use other sensors, you can upload your data here and there, online you can find infos about different housings and so on. Everything can be done in different ways. What is making it one project is the software and the specified hardware you can use with it.
One easily miss some infos in the instructions, check this link:
You can find a list of sensors supported by our firmware
By the way, tubes and pipes are mentioned:
But it could say “Pipes for weather protection, HT Arc DN 75 87°” to be more clear.
Push in sensor into the pipe
Push the parts into the tube, so it’s jammed inside
I agree, the instructions are not very clear! Push the parts into the tube would be really jammed 
It needs to get pushed into the pipes, as I understand it.
Years ago I found this project and where so happy to understand, I can measure PM myself! There are no public measurements close to my place. It took me months before I finally had made my first sensor. Now I teached it once in a school and are planning more classes. It’s open source and open hardware which means, you are free to use it, to change it and do whatever you want with it. Anybody should be aware of the many work nessesary to build this up and keep it running.
“Wow, this project is cool! I want to build a sensor! Does pipe mean the HT arcs? I should connect the BME as shown in the wireing, even if it’s a different sensor with different pinout, right?”
You probably better check the schematic and everything else 
Wrong:
Corrected: